The interferon stimulated gene 20 protein (ISG20) is an innate defense antiviral factor that discriminates self versus non-self translation.
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ABSTRACT:
SUBMITTER: Wu N
PROVIDER: S-EPMC6805002 | biostudies-literature | 2019 Oct
REPOSITORIES: biostudies-literature
Publications
The interferon stimulated gene 20 protein (ISG20) is an innate defense antiviral factor that discriminates self versus non-self translation.
Wu Nannan N Nguyen Xuan-Nhi XN Wang Li L Appourchaux Romain R Zhang Chengfei C Panthu Baptiste B Gruffat Henri H Journo Chloé C Alais Sandrine S Qin Juliang J Zhang Na N Tartour Kevin K Catez Frédéric F Mahieux Renaud R Ohlmann Theophile T Liu Mingyao M Du Bing B Cimarelli Andrea A
PLoS pathogens 20191010 10
ISG20 is a broad spectrum antiviral protein thought to directly degrade viral RNA. However, this mechanism of inhibition remains controversial. Using the Vesicular Stomatitis Virus (VSV) as a model RNA virus, we show here that ISG20 interferes with viral replication by decreasing protein synthesis in the absence of RNA degradation. Importantly, we demonstrate that ISG20 exerts a translational control over a large panel of non-self RNA substrates including those originating from transfected DNA, ...[more]
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Project description:Interferon (IFN) stimulates a whole repertoire of cellular genes, collectively referred to as ISGs (Interferon-stimulated genes). ISG20, a 3´-5´ exonuclease enzyme, has been previously shown to bind and degrade hepatitis B Virus (HBV) transcripts. Here, we show that the N6-methyladenosine (m6A)-modified HBV transcripts are selectively recognized and processed for degradation by ISG20. Moreover, this effect of ISG20 is critically regulated by m6A reader protein, YTHDF2 (YTH-domain family 2). Previously, we identified a unique m6A site within HBV transcripts and confirmed that methylation at nucleotide A1907 regulates HBV lifecycle. In this report, we now show that the methylation at A1907 is a critical regulator of IFN-? mediated decay of HBV RNA. We observed that the HBV RNAs become less sensitive to ISG20 mediated degradation when methyltransferase enzymes or m6A reader protein YTHDF2 are silenced in HBV expressing cells. By using an enzymatically inactive form ISG20D94G, we further demonstrated that ISG20 forms a complex with m6A modified HBV RNA and YTHDF2 protein. Due to terminal redundancy, HBV genomic nucleotide A1907 position is acquired twice by pregenomic RNA (pgRNA) during transcription and therefore the sites of methylation are encoded within 5´ and 3´ epsilon stem loops. We generated HBV mutants that lack m6A site at either one (5´ or 3´) or both the termini (5´& 3´). Using these mutants, we demonstrated that m6A modified HBV RNAs are subjected to ISG20-mediated decay and propose sequence of events, in which ISG20 binds with YTHDF2 and recognizes m6A-modified HBV transcripts to carry out the ribonuclease activity. This is the first study, which identifies a hitherto unknown role of m6A modification of RNA in IFN-? induced viral RNA degradation and proposes a new role of YTHDF2 protein as a cofactor required for IFN-? mediated viral RNA degradation.
| S-EPMC7046284 | biostudies-literature
Project description:Bunyaviruses pose a significant threat to human health, prosperity, and food security. In response to viral infections, interferons (IFNs) upregulate the expression of hundreds of interferon-stimulated genes (ISGs), whose cumulative action can potently inhibit the replication of bunyaviruses. We used a flow cytometry-based method to screen the ability of ?500 unique ISGs from humans and rhesus macaques to inhibit the replication of Bunyamwera orthobunyavirus (BUNV), the prototype of both the Peribunyaviridae family and the Bunyavirales order. Candidates possessing antibunyaviral activity were further examined using a panel of divergent bunyaviruses. Interestingly, one candidate, ISG20, exhibited potent antibunyaviral activity against most viruses examined from the Peribunyaviridae, Hantaviridae, and Nairoviridae families, whereas phleboviruses (Phenuiviridae) largely escaped inhibition. Similar to the case against other viruses known to be targeted by ISG20, the antibunyaviral activity of ISG20 is dependent upon its functional RNase activity. Through use of an infectious virus-like particle (VLP) assay (based on the BUNV minigenome system), we confirmed that gene expression from all 3 viral segments is strongly inhibited by ISG20. Using in vitro evolution, we generated a substantially ISG20-resistant BUNV and mapped the determinants of ISG20 sensitivity/resistance. Taking all the data together, we report that ISG20 is a broad and potent antibunyaviral factor but that some bunyaviruses are remarkably ISG20 resistant. Thus, ISG20 sensitivity/resistance may influence the pathogenesis of bunyaviruses, many of which are emerging viruses of clinical or veterinary significance.IMPORTANCE There are hundreds of bunyaviruses, many of which cause life-threatening acute diseases in humans and livestock. The interferon (IFN) system is a key component of innate immunity, and type I IFNs limit bunyaviral propagation both in vitro and in vivo Type I IFN signaling results in the upregulation of hundreds of IFN-stimulated genes (ISGs), whose concerted action generates an "antiviral state." Although IFNs are critical in limiting bunyaviral replication and pathogenesis, much is still unknown about which ISGs inhibit bunyaviruses. Using ISG-expression screening, we examined the ability of ?500 unique ISGs to inhibit Bunyamwera orthobunyavirus (BUNV), the prototypical bunyavirus. Using this approach, we identified ISG20, an interferon-stimulated exonuclease, as a potent inhibitor of BUNV. Interestingly, ISG20 possesses highly selective antibunyaviral activity, with multiple bunyaviruses being potently inhibited while some largely escape inhibition. We speculate that the ability of some bunyaviruses to escape ISG20 may influence their pathogenesis.
| S-EPMC6002717 | biostudies-literature
Project description:Type I interferon (IFN)-stimulated genes (ISGs) have critical roles in inhibiting virus replication and dissemination. Despite advances in understanding the molecular basis of ISG restriction, the antiviral mechanisms of many remain unclear. The 20-kDa ISG ISG20 is a nuclear 3'-5' exonuclease with preference for single-stranded RNA (ssRNA) and has been implicated in the IFN-mediated restriction of several RNA viruses. Although the exonuclease activity of ISG20 has been shown to degrade viral RNA in vitro, evidence has yet to be presented that virus inhibition in cells requires this activity. Here, we utilized a combination of an inducible, ectopic expression system and newly generated Isg20-/- mice to investigate mechanisms and consequences of ISG20-mediated restriction. Ectopically expressed ISG20 localized primarily to Cajal bodies in the nucleus and restricted replication of chikungunya and Venezuelan equine encephalitis viruses. Although restriction by ISG20 was associated with inhibition of translation of infecting genomic RNA, degradation of viral RNAs was not observed. Instead, translation inhibition of viral RNA was associated with ISG20-induced upregulation of over 100 other genes, many of which encode known antiviral effectors. ISG20 modulated the production of IFIT1, an ISG that suppresses translation of alphavirus RNAs. Consistent with this observation, the pathogenicity of IFIT1-sensitive alphaviruses was increased in Isg20-/- mice compared to that of wild-type viruses but not in cells ectopically expressing ISG20. Our findings establish an indirect role for ISG20 in the early restriction of RNA virus replication by regulating expression of other ISGs that inhibit translation and possibly other activities in the replication cycle.IMPORTANCE The host immune responses to infection lead to the production of type I interferon (IFN), and the upregulation of interferon-stimulated genes (ISGs) reduces virus replication and virus dissemination within a host. Ectopic expression of the interferon-induced 20-kDa exonuclease ISG20 suppressed replication of chikungunya virus and Venezuelan equine encephalitis virus, two mosquito-vectored RNA alphaviruses. Since the replication of alphavirus genomes occurs exclusively in the cytoplasm, the mechanism of nucleus-localized ISG20 inhibition of replication is unclear. In this study, we determined that ISG20 acts as a master regulator of over 100 genes, many of which are ISGs. Specifically, ISG20 upregulated IFIT1 genes and inhibited translation of the alphavirus genome. Furthermore, IFIT1-sensitive alphavirus replication was increased in Isg20-/- mice compared to the replication of wild-type viruses but not in cells ectopically expressing ISG20. We propose that ISG20 acts as an indirect regulator of RNA virus replication in the cytoplasm through the upregulation of many other ISGs.
| S-EPMC6147134 | biostudies-literature
Project description:Hepatitis B virus (HBV) barely induces host interferon (IFN)-stimulated genes (ISGs), which allows efficient HBV replication in the immortalized mouse hepatocytes as per human hepatocytes. Here we found that transfection of Isg20 plasmid robustly inhibits the HBV replication in HBV-infected hepatocytes irrespective of IRF3 or IFN promoter activation. Transfection of Isg20 is thus effective to eradicate HBV in the infected hepatocytes. Transfection of HBV genome or ε-stem of HBV pgRNA (active pgRNA moiety) failed to induce Isg20 in the hepatocytes, while control polyI:C (a viral dsRNA analogue mimic) activated MAVS pathway leading to production of type I IFN and then ISGsg20 via the IFN-α/β receptor (IFNAR). Consistently, addition of IFN-α induced Isg20 and partially suppressed HBV replication in hepatocytes. Chasing HBV RNA, DNA and proteins by blotting indicated that ISG20 expression decreased HBV RNA and replicative DNA in HBV-transfected cells, which resulted in low HBs antigen production and virus titer. The exonuclease domains of ISG20 mainly participated in HBV-RNA decay. In vivo hydrodynamic injection, ISG20 was crucial for suppressing HBV replication without degrading host RNA in the liver. Taken together, ISG20 acts as an innate anti-HBV effector that selectively degrades HBV RNA and blocks replication of infectious HBV particles. ISG20 would be a critical effector for ameliorating chronic HBV infection in the IFN therapy.
| S-EPMC5356548 | biostudies-literature
Project description:Secretion of interferons (IFNs) from virus-infected cells is a hallmark of host antiviral immunity and in fact, IFNs exert their antiviral activities through the induction of antiviral proteins. The IFN-induced protein with tetratricopeptide repeats (IFITs) family is among hundreds of IFN-stimulated genes. This family contains a cluster of duplicated loci. Most mammals have IFIT1, IFIT2, IFIT3 and IFIT5; however, bird, marsupial, frog and fish have only IFIT5. Regardless of species, IFIT5 is always adjacent to SLC16A12. IFIT family genes are predominantly induced by type I and type III interferons and are regulated by the pattern recognition and the JAK-STAT signaling pathway. IFIT family proteins are involved in many processes in response to viral infection. However, some viruses can escape the antiviral functions of the IFIT family by suppressing IFIT family genes expression or methylation of 5' cap of viral molecules. In addition, the variants of IFIT family genes could significantly influence the outcome of hepatitis C virus (HCV) therapy. We believe that our current review provides a comprehensive picture for the community to understand the structure and function of IFIT family genes in response to pathogens in human, as well as in animals.
| S-EPMC3584916 | biostudies-literature
Project description: Not available
| S-EPMC7351677 | biostudies-literature
Project description:BACKGROUND AND AIM:Interferon-stimulated gene 20 (ISG20) is an interferon-inducible exonuclease that inhibits the replication of several RNA viruses. In patients with chronic hepatitis B, ISG20 expression is related to the interferon-? treatment response. However, the molecular mechanism of ISG20-mediated anti-hepatitis B virus (HBV) activity is unclear. METHODS:We have investigated the effect of ISG20 on antiviral activity to address that. The life cycle of HBV was analyzed by the ectopic expression of ISG20 in HepG2 and HepG2-NTCP cells. Finally, to provide physiological relevance of our study, the expression of ISG20 from chronic hepatitis B patients was examined. RESULTS:Interferon-stimulated gene 20 was mainly induced by interferon-? and dramatically inhibited HBV replication. In addition, ISG20 decreased HBV gene expression and transcription. Although ISG20 inhibited HBV replication by reducing viral enhancer activity, the expression of transcription factors that bind the HBV enhancer was not affected. Particularly, ISG20 suppressed HBV enhancer activity by binding to the enhancer II and core promoter (EnhII/Cp) region. CONCLUSION:Our findings suggest that ISG20 exerts the anti-HBV activity by acting as a putative repressor binding to the HBV EnhII/Cp region.
| S-EPMC7497004 | biostudies-literature
Project description:Type I interferon-stimulated genes (ISGs) have critical roles in inhibiting virus replication and dissemination. Despite advances in understanding the molecular basis of ISG restriction, the antiviral mechanisms of many remain unclear. The 20 kDa ISG, ISG20, is a nuclear 3'-5'exonuclease with preference for single stranded RNA (ssRNA) and has been implicated in the IFN-mediated restriction of several RNA viruses. Although the exonuclease activity of ISG20 has been shown to degrade viral RNA in vitro, evidence has yet to be presented that virus inhibition in cells requires this activity. Here, we utilized a combination of an inducible, ectopic expression system and newly generated Isg20−/− mice to investigate mechanisms and consequences of ISG20-mediated restriction. Ectopically expressed ISG20 localized primarily to Cajal bodies in the nucleus and restricted replication of chikungunya and Venezuelan equine encephalitis viruses. Although restriction by ISG20 was associated with inhibition of translation of infecting genomic RNA, degradation of viral RNAs was not observed. Instead, translation inhibition of viral RNA was associated with ISG20-induced upregulation of over 100 other genes, many of which encode known antiviral effectors. ISG20 modulated the production of IFIT1, an ISG that suppresses translation of alphavirus RNAs. Consistent with this observation, the pathogenicity of IFIT1-sensitive alphaviruses was increased in Isg20−/− mice compared to wild-type viruses, but not in ISG20 ectopic-expressing cells. Our findings establish an indirect role for ISG20 in the early restriction of RNA virus replication by regulating expressionof other ISGs that inhibit translation and possibly other activities in the replication cycle.
2018-07-01 | GSE115729 | GEO
Project description:Mesenchymal tumor subpopulations secrete pro-tumorigenic cytokines and promote treatment resistance1-4. This phenomenon has been implicated in chemorefractory small cell lung cancer and resistance to targeted therapies5-8, but remains incompletely defined. Here, we identify a subclass of endogenous retroviruses (ERVs) that engages innate immune signaling in these cells. Stimulated 3 prime antisense retroviral coding sequences (SPARCS) are oriented inversely in 3' untranslated regions of specific genes enriched for regulation by STAT1 and EZH2. Derepression of these loci results in double-stranded RNA generation following IFN-? exposure due to bi-directional transcription from the STAT1-activated gene promoter and the 5' long terminal repeat of the antisense ERV. Engagement of MAVS and STING activates downstream TBK1, IRF3, and STAT1 signaling, sustaining a positive feedback loop. SPARCS induction in human tumors is tightly associated with major histocompatibility complex class 1 expression, mesenchymal markers, and downregulation of chromatin modifying enzymes, including EZH2. Analysis of cell lines with high inducible SPARCS expression reveals strong association with an AXL/MET-positive mesenchymal cell state. While SPARCS-high tumors are immune infiltrated, they also exhibit multiple features of an immune-suppressed microenviroment. Together, these data unveil a subclass of ERVs whose derepression triggers pathologic innate immune signaling in cancer, with important implications for cancer immunotherapy.
| S-EPMC6082722 | biostudies-literature
Project description:BackgroundViruses can impose energetic demands on organisms they infect, in part by hosts mounting resistance. Recognizing that oxygen uptake reliably indicates steady-state energy consumption in all vertebrates, we comprehensively evaluated oxygen uptake and select transcriptomic messaging in sockeye salmon challenged with either a virulent rhabdovirus (IHNV) or a low-virulent reovirus (PRV). We tested three hypotheses relating to the energetic costs of viral resistance and tolerance in this vertebrate system: (1) mounting resistance incurs a metabolic cost or limitation, (2) induction of the innate antiviral interferon system compromises homeostasis, and (3) antiviral defenses are weakened by acute stress.ResultsIHNV infections either produced mortality within 1-4 weeks or the survivors cleared infections within 1-9 weeks. Transcription of three interferon-stimulated genes (ISGs) was strongly correlated with IHNV load but not respiratory performance. Instead, early IHNV resistance was associated with a mean 19% (95% CI = 7-31%; p = 0.003) reduction in standard metabolic rate. The stress of exhaustive exercise did not increase IHNV transcript loads, but elevated host inflammatory transcriptional signaling up to sevenfold. For PRV, sockeye tolerated high-load systemic PRV blood infections. ISG transcription was transiently induced at peak PRV loads without associated morbidity, microscopic lesions, or major changes in aerobic or anaerobic respiratory performance, but some individuals with high-load blood infections experienced a transient, minor reduction in hemoglobin concentration and increased duration of excess post-exercise oxygen consumption.ConclusionsContrary to our first hypothesis, effective resistance against life-threatening rhabdovirus infections or tolerance to high-load reovirus infections incurred minimal metabolic costs to salmon. Even robust systemic activation of the interferon system did not levy an allostatic load sufficient to compromise host homeostasis or respiratory performance, rejecting our second hypothesis that this ancient innate vertebrate antiviral defense is itself energetically expensive. Lastly, an acute stress experienced during testing did not weaken host antiviral defenses sufficiently to promote viral replication; however, a possibility for disease intensification contingent upon underlying inflammation was indicated. These data cumulatively demonstrate that fundamental innate vertebrate defense strategies against potentially life-threatening viral exposure impose limited putative costs on concurrent aerobic or energetic demands of the organism.
| S-EPMC8276435 | biostudies-literature